1. Field of the Invention
The invention relates to the field of diffusers for commercial lighting fixtures and in particular for diffusers capable of providing vertically polarized light, both in the visible and ultraviolet portions of the electromagnetic spectrum.
2. Document Disclosure Program
The application for patent is based on a disclosure filed on Aug. 21, 1992, as Disclosure Document No. 315,781, under the Document Disclosure Program.
3. Description of Prior Art
It has long been recognized that in order to provide glare free illumination, light polarization is essential. By the use of polarized lighting, glare is minimized and contrast is increased. Lighting in most non-residential buildings is largely fluorescent.
Materials that can provide polarized light were a laboratory curiosity until the development of dichroic linear polarizers in sheet form by Land (see for example, LAND, "Polarizers Containing Aligned Crystals of Herapathite", U.S. Pat. No. 1,918,848 (1933)), and by Marks (see for example, MARKS, "Crystalline Formation", U.S. Pat. No. 2,104,949 (1938)).
The linear dichroic polarizers, while useful in many applications, were not suitable for use in commercial lighting fixtures for general illumination purposes. First of all, the polarization was only in one direction. A second major problem was the increase in electrical power needed for lighting as the linear dichroic polarizers absorbed between 60 and 72 percent of the incident light energy being transmitted through them. In particular, the linear dichroic polarizers absorbed most of the ultraviolet light, and much of the purple and blue light in the visible spectrum.
It took the invention of the so called "radial polarizer" by Marks and Kahn in the years after World War II to solve both of these problems (see for example, MARKS, "Multi-layered Light Polarizers", U.S. Pat. No. 3,069,974 (1962) and KAHN "Light Polarizing Structures", U.S. Pat. No. 3,124,639 (1964)).
The invention of the radialens style lighting panel by Jones (see JONES, "Lighting Panel", U.S. Pat. No. 3,829,680 (1974)), provided a diffuser for use in a lighting fixture that could minimize glare from veiling-reflections. This panel contained a continuous pattern of triangular projections, each having three mutually substantially perpendicular surfaces projecting upward towards the light source. The base lines of the mutually perpendicular surfaces are co-planar and the pattern of projections is such that the base lines of all projections on the panel form continuous straight lines directed in specific directions. This results in a light panel which minimizes veiling reflections from the illuminated matter. The panel provides a radial distribution of light with a high lighting efficiency and with a maximum of light in the area which is 30.degree. to 60.degree. from vertical.
Kahn combined the prismatic structure of the JONES Radialens manufactured according to the methodologies and structure of KAHN's polarizing panel (see KAHN, "Light Polarizing Structures", U.S. Pat. No. 3,124,639, (1964), cited above) to obtain the higher visual acuity realized with polarized light with the wider angular distribution of the Radialens panel and the desirable Visual Comfort Probability of 70 or more into an integral structure. What was achieved is not merely the expected advantages of polarized and Radialens light distribution, but also a marked improvement in Visual Comfort Probability and also a reduction in glare at wide angles as disclosed in U.S. Pat. No. 4,796,160 (1989) to KAHN, which is hereby incorporated by reference.
A major problem with the Polarized Radialens and all of the radial multi-layer polarizers manufactured for commercial lighting fixtures is the apparent reduction in brightness. This reduction in brightness is so severe as to be noted by a number of lighting practioners (see, Lovins, Amory, et. al. STATE OF THE ART: LIGHTING, Rocky Mountain Institute, Snowmass, Colo. 81654, (1988), page 157). The objection sometimes encountered with the multi-layer polarized diffusers is that they are so effective that they can give room lighting a "dull" subtly flat quality by suppressing the specular highlights which harsh lighting has led us to expect as visual cues.
Part of this difficulty has been remedied by the inventor's use of full-spectrum fluorescent lamps with multi-layer polarizers (see KARPEN, "Device for Full-Spectrum Polarized Lighting System", U.S. Pat. No. 5,184,881, (1992), (Ser. No. 07/781,844), filed Oct. 24, 1991, allowed Jul. 13, 1992).
An unrecognized problem with all multi-layer polarized diffusers used for commercial lighting fixtures is the type of acrylic plastic used as the supporting material for the polarizer which is adhered to the bottom side of the acrylic sheet. Typically, these multi-layer polarized diffusers are manufactured by extrusion using Type V Series acrylic molding powders as manufactured by Rohm and Haas (Philadelphia, Pa.) or a similar product. The polarizing material is adhered by heat to the bottom of the sheet (see KAHN, "Machine for Continuously Producing Large Area Light Polarizing Panels", U.S. Pat. No. 3,772,128 (1973)). FIG. 1 shows the transmission properties of the Type V Series acrylic molding powder when used to produce an acrylic sheet 0.125 inches thick (taken from Rohm and Haas Technical Bulletin PL-612, (1988)). The light transmission properties of the Type V Series acrylic molding powders is shown for wavelengths between 250 and 450 nanometers. This 0.125 inch thickness is the thickness of the commercially available multi-layer polarized diffusers. The major problem is that the acrylic manufactured from the Type V Series acrylic molding powder transmits less than 50 percent of the ultraviolet light with a wavelength of less than 380 nanometers.
The present invention solves this problem by providing a Type UVT acrylic molding powder or a similar material. The multi-layer polarized diffuser which results from the use of the Type UVT acrylic molding powder is capable of transmitting ultraviolet light with wavelengths as low as 290 nanometers. The resulting transmission of ultraviolet wavelengths all the way down to 290 nanometers provides a substantial improvement in the quality of the illumination.
In addition to solving the problem of absorption of ultraviolet in the 290 to 380 nanometer range, it is noteworthy that none of the patents by Marks or Kahn cited above make any mention of the unrecognized need to polarize the ultraviolet light given off by fluorescent, metal halide, or a number of other light sources as a way of improving the contrast and apparent brightness of objects viewed under a combination of visible and ultraviolet light. The present invention not only transmits the ultraviolet in the 290 to 380 nanometer range, but also polarizes it as well.
4. Theory of the Invention
The key to the present invention is that virtually all paper and textile materials, and many paints and pigments have substances such as optical brighteners that fluoresce under ultraviolet light between 290 and 420 nanometers. The fluorescent effects add to brightness by transforming the ultraviolet radiation between 290 and 420 nanometers into longer wavelength radiation in the visible spectrum (see Barrows, William E., Light, Photometry, and Illuminating Engineering, McGraw-Hill Book Company, New York, (1938), p. 26).
Thus, if the multi-layer polarizers were so modified to be manufactured with an acrylic supporting material that could transmit ultraviolet light so it could be polarized by the multi-layer polarizing material on the bottom of the light polarizing structure, the advantage of the invention is that it would be possible to increase the apparent brightness of paper and textile materials being illuminated by a light source giving off ultraviolet as well as visible light. It should be noted that when compared to an unpolarized light source, the ultraviolet light will be vertically polarized as well, so it will be glare free, as it is well known that glare from unpolarized radiation is detrimental to one's eyes and the ability to see.
FIG. 1 also shows the transmission properties of an ultraviolet transmitting acrylic made from an acrylic molding powder such as the UVT type acrylic molding powder as manufactured by Rohm and Haas (taken from Rohm and Haas Technical Bulletin PL-612e, (1985), p. 5) from 250 to 450 nanometers. It should be noted that acrylic sheets manufactured from this acrylic molding powder will transmit 85 percent of the ultraviolet light with a wavelength greater than 315 nanometers.
Thus, the application of an ultraviolet transmitting acrylic would permit the transmission of the ultraviolet light emitted from a light source through the supporting acrylic so the ultraviolet light would then be polarized by the multi-layer polarizing materials which are adhered to the bottom of the acrylic sheet, which is the side of the sheet facing towards the objects being illuminated.
It should be noted that ultraviolet light is not detectable by a standard photopic light meter which measures visible light according to the Standard Observer Curve (.lambda.) as established by the International Commission on Illumination. Thus, using the present invention, objects will appear brighter, even though the measured foot-candles will be virtually the same for a light source in the visible as compared with a light source which emits the same visible light plus some ultraviolet light. It will then be necessary to develop new photometric instruments that will integrate the fluorescent effects of ultraviolet light into the Standard Observer Curve V(.lambda.) for the photopic region.
It is also not generally known that the eye responds to ultraviolet light. In the young healthy eye the ocular media are sufficiently transparent to allow a substantial amount of ultraviolet energy (so-called "invisible") of wavelength as short as 350 nanometers to reach the retina and evoke a visual sensation. Smaller amounts of wavelengths as short as 300 nanometers may be transmitted, but this effect is not important in ordinary vision at high levels of luminance (see The Science of Color, Optical Society of America, Washington, D.C. (1953), p. 76).
Therefore, since my invention provides an increase in ultraviolet illumination in polarized lighting installations, there will be an increase in visual sensation for normal healthy eyes.
Most fluorescent lamps produce a certain amount of ultraviolet light, and many of the spectra of such lamps contain a peak in the ultraviolet at 365 nanometers. Full-spectrum lamps are defined as lamps having a color rendition index of 90 or above and a correlated color temperature of 5,000 degrees Kelvin or above. The visually effective F40/T12 Color Classer 75, with a correlated color temperature of 7,500 degrees Kelvin, and a color rendition index of 93, is a full-spectrum fluorescent lamp currently available from Duro-Test Corporation, Fairfield, N.J., and provides illumination not only in the visible range from 380 to 780 nanometers, but also provides a significant amount of ultraviolet light from 290 to 380 nanometers. This ultraviolet light is exactly the radiation capable of producing fluorescent effects.
Thus, the use of the Type V Series acrylic molding powder in the manufacture of the supporting layer for the multi-layer polarizing material eliminates much of the benefit of the ultraviolet light in improving the apparent brightness of paper and textile objects since a multi-layer polarized diffuser made from the Type V Series acrylic molding powder or a similar product would absorb most of the ultraviolet light between 290 and 380 nanometers.
FIG. 2 shows the spectral energy distribution of the F40/T12 Color Classer 75 fluorescent lamp, as provided to the inventor by the Duro-Test Corporation. As shown, there is production of much ultraviolet light between 290 and 380 nanometers.
In comparison to the Type V Series acrylic molding powder which absorbs much of the valuable ultraviolet light, use of the Type UVT acrylic molding powder or a similar product in the manufacture of the supporting acrylic of the multi-layer polarized diffuser would then allow almost all of the valuable ultraviolet light emitted from lamps between 290 and 380 nanometers to pass through the acrylic supporting structure and hence the ultraviolet light would be then vertically polarized where it could increase the apparent brightness of paper and textile materials without the harmful glare that results from unpolarized ultraviolet as well as unpolarized visible light.
The polarization effects would be expected to be greater in the ultraviolet than in the visible portion of the electromagnetic spectrum. It is known that the index of refraction of many materials varies with the wavelength of light, and the index of refraction increases with a decrease in the wavelength of light (see, for example, Halliday, David, and Resnick, Robert, Physics, John Wiley & Sons, New York, 1966, p. 1014-1015). As the index of refraction increases, the amount of polarization increases, especially for multi-layer type polarizing type materials. The multi-layer polarizers provide vertically polarized visible and ultraviolet light by means of reflection and refraction; the polarization effects are greater with an increase in the index of refraction, hence the degree of polarization will be greater in the ultraviolet region as compared with light in the visible portion of the spectrum.
It is also known that the ultraviolet light which is scattered in the sky is very highly polarized (see, for example, Feynman, Richard, et. al., The Feynman Lectures on Physics, Volume I, Addison-Wesley Publishing Company, Reading, Mass., (1963), p. 32-8). The scattering of ultraviolet light increases as the fourth power of the frequency of the spectrum. Thus, one should expect that the sky should be blue, since the blue light is more highly scattered than the light at the red end of the spectrum. This scattering is known as the Raleigh scattering in honor of the person who first discovered it. Daylight contains radiation down to 290 nanometers (see, Duffie, John, A. et. al., Solar Energy Thermal Processes, John Wiley & Sons, New York, 1974, p. 14, and Cayless, M. A., and Marsden, A. M., Lamps and Lighting, Edward Arnold, London, 1983, p. 4). Thus, the present invention of an ultraviolet transmitting polarized diffuser, when used in conjunction with full-spectrum fluorescent lamps, will provide a lighting system which is substantially duplicates natural daylight, and which contains vertically polarized ultraviolet light in addition to vertically polarized visible light. The previously available multi-layer polarized diffusers which are made from a Type V Series or similar acrylic molding powder block much of the ultraviolet light with wavelengths below about 380 nanometers.
An example of the use of the present invention which in no way limits its potential application is for the production of so called "north sky" lighting that artists prefer. In north sky lighting, one combines a 7,500 degree fluorescent lamp with an ultraviolet transmitting multi-layer polarized diffuser. A multi-layer polarized diffuser made from the Type V Series acrylic molding powder or a similar material would produce an inferior "north sky" effect due to the absence of ultraviolet light below 380 nanometers.
Passage of the ultraviolet light through the acrylic supporting layer of the present invention and through the multi-layer polarizer will reduce degradation of the acrylic materials, since the ultraviolet light is passing through the diffuser, rather than having an opportunity to interact with it. Thus, the need for periodic replacement of the lighting diffusers is reduced significantly, along with a reduction of the solid waste that would otherwise be added to the solid waste stream when materials are discarded in the trash.
Another benefit of the use of an ultraviolet transmitting polarized diffuser (as compared to ultraviolet absorbing polarized diffusers of the prior art) is the energy saving potential. Since objects will appear brighter due to fluoresce effects, one can install fewer lighting fixtures and spread them farther apart.
A secondary energy savings occurs because when the Type V Series acrylic molding powder is used to manufacture the multi-layer polarizer, the acrylic absorbs the ultraviolet light and is ultimately converted to heat. The diffuser heats up, which traps the heat from the fluorescent lamps inside the fixture. By allowing the ultraviolet light to easily pass through the ultraviolet transmitting multi-layer polarizer, additional heat can be rejected from the lighting fixture, and the heat build-up is reduced significantly, lowering the lamp operating temperature. It is known that reduced light output from a fluorescent fixture results from operating a fluorescent lamp above its optimum lamp wall temperature (see Jerome, Charles W., "Effect of Bulb Wall Temperatures on Fluorescent Lamp Parameters", Illuminating Engineering, February, 1956, pp. 205-213).
It has been shown by Cobb (see, Cobb, Percy W, and Moss, Frank E., "Lighting and Contrast", Transactions of the Illuminating Engineering Society, February, 1927, p. 195-204, also see Marks, Alvin, "Multilayer Polarizers and Their Application to General Polarized Lighting", Illuminating Engineering, February 1959 p. 127) that visual acuity increases with contrast. Marks provided proof using a set of algebraic equations that contrast will always be improved using polarized illumination. With the use of the ultraviolet transmitting multi-layer polarizer, contrast, and hence visual acuity, will be greater than when using a multi-layer polarizer with a supporting acrylic made of a Type V Series acrylic molding powder or a similar material, since the effect of the ultraviolet light will be to increase brightness of the paper which contains the optical brighteners which fluoresce under ultraviolet light. Note that the areas of paper covered by black print will not fluoresce, so there will be a definite increase in contrast between the print and the paper it is printed on when compared to illuminating the same paper with a light source giving off ultraviolet light and having the ultraviolet light blocked by a multi-layer polarized diffuser made of the Type V Series or similar acrylic molding powder.
A novel use of the ultraviolet transmitting multi-layer polarized diffuser would be for illumination using so called "black lights" that only give off ultraviolet light. Lighting fixtures using the ultraviolet transmitting polarized diffuser could be used for special effects lighting for nightclubs and other places of entertainment. As mentioned above, use of the ultraviolet transmitting multi-layer polarizer with an ultraviolet light source with provide vertically polarized ultraviolet light, as it is well known that glare from unpolarized radiation is detrimental to one's eyes and the ability to see.